Electric circuit for photoelectric engraving machines



Feb. 23, 1943. G. E. Losll-:R ET AL 2,312,042

ELECTRIC CIRCUIT FOR PHOTOELECTRIC ENGRAVING MACHINES Filed Aug. 3, 1940 2 Sheets-Sheet l m fw @JW INVENTORS Lam #v/165 ATTORNEY.

Feb- 23, 1943 G. E. LoslER ET Al. 2,312,042

ELECTRIC CIRCUIT FOR PHOTOELECTRIC ENGRAVING MACHINES 2 Sheets-Sheet 2 w ME w 4` 1 V O N mv w PG .v 5 m A@ mw Nv NR vom mom m@ b@ MNT W|J mF/h TH|,M.\ v Mau 5%. vw@ www, Kw2 E.: ./mm llll... 4 E U v5 Q@4 m \O\ Nt uw NQ BY www /A @has Fe/'f ATTORNEY Patented Feb. 23, 1943 ELECTRIC CIRCUIT FOR PHOTOELECTRIC ENGRAVING MACHINES George E. Losier, Bloomfield, and Leo V. Skinner, Newark, N. J.

Application August 3, 1940, Serial N0. 350,428

(Cl. P18-6.6)

2 Claims.

The present invention relates to an electrical systemfor a photo-electric half-tone engraving machine of the type shown and described in Losier Patents No. 2,092,764 and 2,092,765 and to the method of operating such a machine with an electrical system shown and described herein to illustrate the present invention.

Reference is hereby made to said patents, Numbers 2,092,764 and 2,092,765 for a showing and description of a photo-electric half-tone engraving machine suitable for use in the practice of the present invention, including a cutting head which is described generally herein, reference being made also to said patents for specific disclosures of the cutting head generally described.

An object of the present invention is to provide an electrical system for a photo-electric half-tone engraving machine, which electrical system comprises two separate sources of power, one source of power for operating the cutting tool with a constant length of its reciprocating strokes whatever the depth of its entrance into the material being cut (whether for light, intermediate or dark shades of reproduction), and the other source of power for changing the mean point of the reciprocating strokes in accordance with the depth of the tools entry into the material being cut as the various tones of light and shade are being reproduced.

Reference is hereby made to Patent Number 2,032,541 issued March 3, 1936, to applicant Losier for a description of a half-tone printing plate such as can be cut with the machine and ap.

paratus of the present invention.

In the accompanying drawings, showing illustrative embodiments of the power circuits of the present invention,

Figure l is a diagrammatical view showing one embodiment of the power circuits of the present invention, with certain directly cooperative parts from the disclosure in said U. S. Patent Number 2,092,764 shown in part and by diagrammatic representation;

Figure 2 is a diagrammatical view, similar to that of Figure 1, but showing an alternate embodiment of that part of the circuit which varies the mean position of the cutting stroke; y

Figure 3 is a diagrammatic view showing an alternate embodiment of means shown in Fig--l ure l for generating an alternating current which, when amplied, produces constant length stroke of the cutting tool;

Figure 4 is a vertical sectional view of a halftone printing plate indicating somewhat diabattery II and said cathode I3.

grammatically the substantially uniform length of the stroke of the cutting tool at different depths of cut and for strokes in which the tool does not enter the metal.

Referring now to Figure 1 of thedrawings, the picture carrier I (corresponding to picture carrier I4 of Fig. 1 in said Patent Number 2,092,765) carries a picture 2 to be reproduced. A light beam from a constant source of light 3 illuminates said picture 2 and, by reflection from said picture 2, passes through a lens system (not shown) where it concentrates and from which it passes to a light stop 4 having a small opening 5. A very small portion of said light beam passes through said opening 5 and to the cathode 6 of a photo-electric cell 1. A lead 8 from said cathode 6 of said photo-electric cell 1 connects to one side of a resistor 9, the other side of which latter connects by a lead I to the negative side of a battery II the positive side of which latter connects through a lead I2 to the cathode I3 of an amplifying tube I4, with a connection to ground I on said lead I2 between said The plate I6 of said amplifying tube I4 connects through a lead I1 to the grid I8 of the power tube I9. A lead connects from the cathode 2I of said power tube I9 to the cathode 22 of the power tube 23. The grid 24 of said power tube 23 connects through lead 25 to the plate 26 of the am` plifying tube 21, and a lead 28 connects the cathode 29 of said amplifying tube `21 to said lead I2. The grid 3| of said amplifying tube I4 connects through a lead 32 to said lead 8.

A lead 33 connects said lead I1 to one end of a resistor 34, the other end of which latter connects through a lead 35 then through a resistor 36 to said lead 25.

The plate 31 of said power tube 23 connects through a lead 38 to one end of the xed armature coil 39 of the cutting head 40, and the other end of said armature coil 39 connects through a lead 4I to the plate 42 of said power tube I9. The `mid-point of said armature coil 39 connects through a lead 43 to the positive side of a battery 44, the negative side of which connects to said lead 20.

A lead 45 connects said lead 20 to an adjustable contact 46 on a bank of batteries 41 and another adjustable contact 46 on said bank of batteries 41 connects by way of lead 49 to the anode (not shown) of said photo-electric cell 1.

The grid 50 of said amplifying tube 21 connects to the negative side of a battery 5I, the positive side of which connects to-an adjustable contact 52 on said resistor 34 between the said Y ends thereof to which said leads 33 and 35 conneet.

A lead 53 connects said lead 35 to the positive end of said bank of batteries 41, and a lead 54 connects the negative end of said bank of batteries 41 to said ground I5.

An oscillatory amature 68, mounted within said stationary amature coil 39, carries at one near the` latters outer end and holds said cutting f tool 62 for movement in a straight line substantially vertically with respect to the surface of said plate 83 while said surface is being cut into. A permanent magnet 86 diagrammatically shown, through its two pairs of poles 81, 81 and 68, 88, provides a field which passes through said armature 88. Said cutting tool 82 is a V-shaped tool such as is described in said Losier Patent 2,032,541 to which reference is hereby'made for a detailed description of said cutting tool 82 hereof (cutting tool I8 in the drawing and description of said Losier Patent Number 2,032,541).

As described in said Patent Number 2,092,765 said picture carrier |A and said plate carrier84 are moved synchronously in reciprocating motion. I

Said plate carrier 84 carries a transparent film 18 which has opaque lines 1I, 1| thereon which extend at right angles to the line of `movement of said lm 18 with said plate carrier- 64. Said opaque lines 1 I, 1| are of accurate uniform width and are accurately spaced apart at a uniform distance equal to their width whereby there are left between them transparent lines 12, 12 of accurate, uniform width, accurately and uniformly spaced apart from each other by said opaque strips 1|, 1|. The widthiof each of said opaque lines 1|, 1I and of transparent lines 12, 12 is accurately predetermined and made to be equal to the distance between the centers of the dots or printing areas of the half-tone reproduction to be cut on said plate 83.

Mounted at one side of said transparent nlm 18 is a fixed constant source of light 13 and on the opposite side of said transparent film 18 is a fixed photo-electric cell 15 in operative relation to receive light through said transparent film 18 from said source 13, with a fixed lightunit 18 parallel to said lines 1|, 12 and between them and said source of light 13 and of predetermined size to admit a light beam at said transparent film 18 of a width equal to the width of said lines 1|,'12.

The cathode 11 of said photo-electric 'cell 15 connects through a lead 18 to one side of a resistor 19 the other side of which latterconnects through a lead 88 to said lead I2 and therebyto said ground I and through said lead 54 to the negative end of said bank of batteries 41. 'I'he anode (not shown) of said photo-electric cell connects through lead 8| to an adjustable con-V tact 82 on said bank of batteries 41.

A lead 83 from said lead 18 connects to one side'of a condenser 84 and a lead 85 connects from the other side of said condenser 84 to a grid 88 of an amplifying tube 81. The cathode 88 of said amplifying tube 81 connects through a lead 83 to said lead 54 and thereby tosaid ground Iii.` A lead 98 from said lead 85 connectsv through 75 a resistor 9| and thence through lead 92 to the negative side of a battery 93, the positive side of which connects through a lead 94 to said lead I2 to-said ground I5.

It is to be noted `that all leads connecting to said lead I2 connect both to said ground l5 and to the negative end of said bank of batteries 41.

A lead 95 from said lead 89 connects to the negative end of a battery 95, the positive end of which connects through the lead 91 to mid-point of the primary coil 98 of the output transformer 9,9. Oneend of said primary coil 98 connects through the lead |88 to. the plate |8| of the power amplifying tube |82. The other end of said primary coil 98 connects through the lead |83 to the plate |84 of the power amplifying tube |85.- Lead |88 connects the cathode |81 of said power amplifyingtube -I82 to said lead 95 Vand lead |88 connects the cathode |89 of said amplifying power tube to said lead 95. The

grid ||8 of said power tube |82 connects through lead to one end of the secondary coil ||2 of the transformer ||3, the other end of said secondary coil |I2 connects through the lead |I4 to a grid |I5 in said power tube |85. A lead ||8 connects from the mid-point of said secondary coil ||2 to the negative end of the battery II1, the positive end of which connects through the lead ||8 tosaid lead 95.

It can be seen that said transformer II3, battery |I1, power tubes |82 and |85 and transformer 99 are connected in push-pull relation, the purpose of which will be hereinafter de-' scribed.

One end of the secondary coil I I9 of said transformerl 99 connects through'the lead |28, to one side of the condenser |2I, the opposite side of which connects through the lead |22 to said lead 38. The other end of said transformer secondary ||9 connects through the lead |23 to said lead 4I. A lead |24 connects from said lead 23 to one side of a condenser |25 the other side of which connects through the' lead |26 to said 1ead |22.

` One end of the primary coil |21'of said transformer ||3 connects through the lead |28 to the` plate |29 of the amplifying tube |38, the grid |3| of which connects through the lead |32 to one side of a condenser |33 the other'side of which connects through the lead |34 vto the plate |35 of said amplifying tube 81. The other side of' said primary coil |21 connects through the lead |35 to one side of a resistor |31, the other side of which connects through the lead |38 to said lead |34. The cathode |39 in said amplifying tube |38 connectsthrough lead |48 to said lead 95. The lead |4| connects said lead 95 to the i positive side of a battery |42, the negative side of which connects through the lead |43 to one end of a resistor |44, the opposite end of which connects through lead |45 to lsaid lead |32. A

lead |45 connects saidlead |35 to said lead 53;/ and thereby to the positive side of said battery 41. Y

Each of said tubes I4, I9, 23, 21, 81,'I82, |85

and |38 have heating `filaments conventionally shown but not numbered.

Referring now to .Figure 2 of the drawings. there is shown an alternative form of scanning system and amplifying circuit therefor.v There is shown in Figure 2 the picture carrier I, picture 2, constant light source 3, photo-electric cell 1 and cutting head 48 of Figure 1 together with said photo-electric cell,11, said transformer ||3 and said transformer 89 with the circuit therebetween for producing the regularly timed cutting stroke of said cutting head 40 somewhat as shown in Figure 1 but somewhat structurally modified as hereinafter described. Said armature coil 39 of said cutting head 40 is connected to said battery 44 and said power tubes |9 and 23 in push-pull relation as in Figure 1. But it is to be understood that either timing circuit (that of Fig. 1 or of Fig. 2) can be used with either of the scanning circuits (Fig. 1 or Fig. 2).

In Figure 2 the ends of a metallic ribbon loop |50 of a. light valve |5|, mounted between said picture 2 and said photo-electric cell 1, and connected respectively by the leads |52, |53 to the terminals of the alternating current generator |54 so that when current from the latter passes through said metallic ribbon loop |50 the latter opens and closes in regular timed movement, synchronous with the current from said generator |54, so that when said current is at a maximum in one direction the loop is closed and shuts oif the light from said constant source 3 and when said current is ata maximum in the opposite direction said metallic ribbon loop |50 is open to a maximum position and lets a maximum amount of light, reflected by a scanned point on said picture 2, pass from said constant source 3 to said photo-electric cell 1. Between the maximum open position of said metallic ribbon loop |50 and its closed position the resistance of said photo electric cell 1 varies with a pulsating characteristic. When a darkportion of said picture 2 is being scannedsaid pulsating characteristic will have a very small amplitude, and when a high-light portion of said picture 2 is being scanned saidl pulsating characteristic will have a much greater amplitude. The effect of this variation is characteristic on said cutting head B6 will be hereinafter described. Also for purposes hereinafter described the current from said alternating current generator |54 is of a frequency several unit multiples of the frequency of the regularly timed cutting lstroke circuit described above for Figure 1 and hereinafter described for Figure 2 in a somewhat modified alternate form. Said alternative current generator |54 can be a vacuum tube oscillator or a rotating armature generator or other equivalent and in Figure 2 is conventionally shown.

As in the circuit of Figure 1, said lead 49 connects the anode (not shown) of said photo-electric cell 1 to said adjustable contact 48 on said battery 41. Said lead 8 connects said cathode 6, through lead |55, to one end of a resistor |56, the other end of which connects through the lead |51 to said lead 80 and thereby to said ground |5 and to the groundedside of said battery 41. Said lead 8 also connects through a lead |58 to one side of a condenser |59 the other side of which connects through a lead |60 to the grid |6| of the amplifying tube |62. A lead |63 connects said lead |51 to said lead 20 and to the negative side of said battery 44. The plate |64 of said amplifying tube |62 connects through a lead |65 to one side of a resistor |66 the other side of which connects through a lead |61 to the positive side of said battery 41. The cathode |68 of said amplifying side of a resistor |16 the other side of which connects through a lead |11 to said lead |63.

An adjustable contact |80 on said resistor |66 connects through a lead |8| to one side of a condenser l82, the other side of which connects through a lead |83 to the-grid |84 of the amplifying tube |85. A lead |86 connects said lead |83 to one side of the resistor |81, the other side of which connects through the lead |88 to said lead |63. A lead |89 connects the cathode |90 of said amplifying tube |85 to one side of a resistor tube |62 connects through lead |69 to one side of y a resistor |10, the other side of which connects through lead |1| to said lead |63. A lead |12 connects one end of said resistor |10 to one side of a condenser |13, the other side of which connects through a lead |14 to the other side of said resistor |10.

A lead |15 connects from said lead |60 to one |9I, the other side of which connects through a leadi|92 to said lead |63. A lead |93 connects from one side of said resistor |9| to one `side of a condenser |94 the other side of which connects through a lead |95 to the other side of said resistor |N9|.

A lead |91 connects the plate |98 of said amplifying tube to the one end of primary coil |99 of the transformer 200 the other end of weh'ich connects through the lead 20| to said lead One end of the secondary coil 202 o-f said transformer 200 connects through a lead 203 to the plate'204 of the detector tube 205, and the other end of said secondary coil 202 connectsithrough a lead 206 to an adjustable contact 201 dn a battery 208, the positive side of which connects through a lead 209 to'said grid 24 of said power tube 23. The said grid I8 of said power tube |9 connects through a lead 2|0 to the negative side of a battery 2|| and an adjustable contact 2|2 on said battery 2|| connects through a lead 2|3 to the cathode 2|4 of said detector tube 205. As in Figure 1, said lead 20 connects said cathode 2| of said power tube I9 to said cathode 22 of said power tube 23.

A lead 2|5 connects said lead 2|3 to one end ofa resistor 2|6 the other end of Which connects through a lead 2|1 to said lead 206. A lead 2|8 connects the mid-point of said resistor 2|6 to said lead |63. A lead 2|9 connects said lead 2|5 to one side of a condenser 220, the other side of which connects through the lead 22| to said lead 2|8. A lead 222 connects said lead 206 to one side of a condenser 223, the other side of which connects through a lead 224 to said lead 2|8.

As in Figure 1, said plates 31 and 42, of said power tube 23 Iand I9, respectively connect `through leads 38 and 4|, respectively, to opposite ends of said armature coil 39, and said lead 43 connects the mid-point of said armature coil 39 to the 'positive end of 'said battery 44.

Also as in Figure 1, said cathode 11 of said photo-electric cellv 15 connects successively through said lead 10, resistor 19 and lead 80 to said ground |5 and said lead 8| connects said anode (not shown) of photo-electric cell 15 to said adjustable contact 82 on said battery 41. Said lead 18 connects successively through lead 83, condenser 84 and lead 85 to said grid 86 of said amplifying tube 81.

A lead 225 connects from said lead 85 toone side of a resistor 226 the other side of which connects through a lead 221 to said lead 80. A lead 228 connects said lead 221 to the negative side of said battery 96, the positive side of which connectsthrough the lead 91 to the mid-,point of said prim-ary coil 98 of said transformer 99. Said lead |00 connects one side of said primary coil 98 to said plate |0| of said power tube |02 and said lead |03 connects the other end of said primary coil 98 to said plate |04 of said power tube |05. Said lead |08 connects said cathode |01 of said power tube |02 to said cathode |09 of said power tube |05, and, therebetween, connects to said lead 228.

Also as in Fig. 1 said lead connects said grid I I of said power tube |02 to one end of said secondary coil H2 of said transformer H3, the other end of which connects through said lead H4 to said grid H5 of said power tube |05. The said lead H8 connects the mid-point of said secondary coil H2 to the negative side of said bat-I tery H1, the positive side of which `connects through lead ||8 to said lead 228.

As in Fig. l, said secondary coil H8 of said transformer 88 connects through said leads |22 and |23, respectively, to said leads 38 and -4|, with said condensers |2| and |25 in series and in parallel, respectively. Said amplifying tube |30 is connected in series betweenone side of said primary coil |21 of said transformer H3, through saidleads |28, |32 and |34, with said condenser |33 in series between said grid |3| of said amplifying tube |30 and said vplate |35 of said amplifying tube 81. The other side of said primary coil |21 connects through said lead |38 to the positive end of said battery 41. Said resistor |31 and lead |38- are connected as shown in Fig. l.

Said cathode |38 of said amplifying ,tube |30 connects successively through lead 230, resistor 23| and lead 232 to said lead 228, with lead 233, condenser 234 and lead 235 connecting successively from one side of said resistor 23| to the other side thereof.

Lead 238, resistor 2 31 and lead 238 connect successively from said lead |32 to said lead 228.

' Said cathode 88 of said ampifying tube 81 connects successively through lead 238, resistor 240, and lead 24| to said lead 228, with lead 242, condenser 243 and lead 244 connecting successively from one side of said resistor 240 to the other side thereof. 1

As in the tubes of Figure 1, said tubes |82, |85,

205, I8, 23, |05, |02, |30 and 81 have heating filaments conventionally shown but not numbered and without showing the necessary source of heating current.

In Figure 3 is shown alternative means for producing a regularly varying current in the system connected to said leads 18 and 8|, and this alternative means includes a rack 250iixed to and movable with said plate carrier 84, a pinion 25| in operated engagement and relation to said rack 250, a shaft 282 which is driven by said pinion,

25| and which drives a current generator -253 which produces a current similar to that supplied to said leads 18 and 8| in the system of Figure 1 as above described.

The -following is a description of the use and operation of the apparatus of Figure 1 for scanning a picture and using an effect of the scanning operation to produce a machine cut halftone printing plate.

Said plate 63, to be cut to make a half-tone printing plate, is placed on said plate carrier 84 and fixed thereon in a suitable manner not shown and said picture 2, to be reproduced, is

rupt the beam-of light passing from said constant source of light 13 through said light slit 18 to said photo-electric cell 15, whereby the resistance of said photo-electric cell 15 is repeatedly and regularly varied between a minimum value and a maximum value. As a result of this regularly repeated variation in the resistance of said photo-electric `cell 15, the current passing therethrough from said battery 41 by way of said leads 18, and 8| and said resistor 18 will vary in a similar manner and the shape of the current-time curve or graph will be substantially saw-tooth.

VIt can be seen that a regularly varying current will be flowing through said resistor 18 and that there will be a voltage drop across the terminals of said resistor 18 Whose value varies regularly and proportionally to the value of said current.

Now, said cathode `88, `being heated by the tube filament, will supply a stream of electrons which are attracted to said plate |35 because of the latters positive potential with respect to said cathode 88 as determined by the connection oi' said plate |35 through said resistor |31 to the positive side oi said battery 41 and the connection of said cathode 88 to the negative side of said` battery 41, -as above described.

It will also be seen that battery 83 will produce a predetermined potential between said cathode 88 andsaid grid 86 in which said grid 88 is negative with respect to said cathode 88 and that the regularly repeated variations in the voltage drop across said resistor 18 will produce a proportional regularly and repeatedly varying voltage between each of the plates of said condenser 84 and said 4ground |5 with the result i that there will be a regular variation in the voltage between said cathode 88 and said grid 88 and a consequent regular variation in the quantity of electrons iiowing from said cathode 88 to said plate |35.

Said tube 81 being an amplifying tube, as above set forth, it will be seen that the regularly repeated voltage drop across resistor 18 will be Vreproduced and amplified in the voltage drop across said resistor |31. This voltage drop across said resistor |31 will produce a proportional regularly and repeatedly varying-voltage 'between each condenser plate of said condenser v|33 and said ground Il, with the result that there will be a vregular variation in the voltage between said cathode |38 and said grid |3| and a consequent regular variation in the quantity of electronsv ilowing from said cathode A|38 to said plate |28 of said amplifying tube |30. Said grid |3| is kept at a predetermined potential with respect to said cathode |38 by the voltage impressed by said battery |42 through said resistor |41.

Said tube |30 being an amplifying tube, as above set forth, it will lbe seen that the regularly repeated voltage drop across said resistor |31 will be reproduced and amplified in the voltage drop across said primary coil |21l of said transformer H3, said primary coil |21 being included in the circuit which comprises the said primary coil |21, said plate |28,.said cathode |38, said battery 41 and the various leads completing said circuit.

It can be seen then that said voltage variations in said primary coil |21 will induce corresponding voltage variations between said lead and said lead ||4 of said'secondary coil H2, one half-of which, at any given instant, is between said lead and said lead H8 and the other half of which is between said lead H8 and said lead H4. Said battery I|1 having its negative side connected to said lead H6 and its positive side connected to said lead H8, said grid of said power amplifying tube |02 and said grid I of said power amplifying tube |05 will be kept at predetermined potential variations with respect to said cathode |01 and said cathode |09 respectively, because, when there is no voltage drop across said secondary coil H2, said battery H1 will place a fixed voltage between said grid H0 and said cathode |01 and between said grid l I5 and Said cathode |09.

Also, when there is no voltage drop across said secondary |I2, said cathodes |01 and |09 being heated, the current from said battery 96 through said lead 91 will divide equally between the halves of said primary coil 98 of said transformer 99, but when there is a varying voltage drop across said secondary H2 the currents flowing through said halves of said primary coil 98 will vary in opposite relation so that when current in one half is increasing the current in the other half is decreasing, and vice versa, according to the phase of the voltage in said secondary coll H2, with the result that there will be produced a regularly varying voltage drop across said primary coil 98 which is an amplified reproduction of the varying voltage drop across said secondary coil H2 and of the varying voltage drop across said resistor 19. This varying voltage drop across said primary coil 98 is reproduced in said secondary coil H9 and transmitted to said armature coil 39 whereby said armature 60 is actuated on its axis with an oscillatory movement which is regularly timed with and by the interruptions by said transparent lm of the beam of light from said constant source 13 to said photo-electric cell 15, so that said cutting tool 62 is caused to have a regularly reciprocating stroke of constant length.

Said condenser |25 is of such a value that the circuit comprising said secondary coil H9, condenser |2I, armature coil 39 and condenser |25 will be tuned to resonance with the regularly repeated variations in voltage drop across said secondary coil H9 and corresponding regularly repeated variations in current ow through said armature coil 39.

The function of said condenser |2| is to prevent any direct current from said battery 44 from passing through said 'secondary |20 of said transformer 99.

As hereinafter described, said cutting'tool 62, during its movement with a regularly reciprocating stroke of constant length, is controlled so that the lower limit of its reciprocating stroke is varied in accordance with the lights and shades of a picture 2 being scanned on said picture carrier I.

Said -picture 2 being moved with a reciprocating motion synchronous with the motion of said plate 63 and said transparent film 10, the light passing from said constant source 3 to said cathode 6 will vary in accordance with the variations in light and shade of said picture 2 and thereby cause corresponding variations in the internal resistance of said photo-electric cell v1 and in turn cause variations in the amount of current flowing from said battery 41 through said resistor 9 and thereby variations in the voltage drop across said resistor '9 which are impressed between said grid 3| and cathode I3 of said amplifying tube I4. Said battery Il keeps said grid 3| at the proper operating potential with respect to said cathode I3. Said variations in potential between said grid 3| and cathode I3 are reproduced and amplied in the voltage drop across said resistor 34 due to the current owing from said battery 41 through said resistor 34, plate I6 and cathode I3. Said variations in potential across said resistor 34 are impressed between said grid |8 and cathode 2| of said power amplifying tube I9 and are reproduced and amplified in the current flowing from said battery 44 through one-half of said armature coil 39 and thence from said' plate 42 to said cathode 2|.

Said battery 5| keeps said grid 50 of said amplifying tube 21 at the proper operating potential with respect to said cathode 29 by overcoming the difference between the voltage drop in that part of said resistor 34 between said adjustable contact 52 and lead 35, caused by current owing from said battery 41, plus the voltage of said battery 41, with an additional voltage suflicient to keep said tube I4 operating at its proper grid potential. The potential between said lead 35 and said adjustable contact 52 is a fraction of the total voltage across said resistor 34 and varies in accordance with variations in said total voltage across said resistor 34 and is impressed between said grid and' said cathode 29. The variations in voltage impressed between said grid 50 and cathode 29 are reproduced and amplified in the current owing from said battery 41 through resistor 36 and said plate 2.6 to said cathode 29. K

In a similar manner, the voltage drop across said resistor 36 is impressed between said grid 24 and cathode 22 of said power amplifying tube 23 and is predetermined to be equal at any instant to but opposite in phase to said voltage drop impressed between said grid I8 and said cathode 2| so that said power tubes I9 and 23 operate in push-pull relation.

Said picture 2, plate 63 and transparent lm 10 being in synchronous motion, the regularly timed interruptions of light beam falling on said photo-electric cell 15 caused by said transparent 111m 10 will cause said armature 60 and said cutting tool 62 to have la regular up and down motion of a predetermined and constant amplitude or distance, and the variations of light and shade of said picture 2 will cause corresponding variations in the value or strength of the light passing from said constant source 3 to said photoelectric cell 1 and thereby will cause said armature and said cutting tool 62 to have a varying up and down motion of amplitude or distance corresponding to the said variations in the light and shade of said picture 2. The resultant of said regular up and down motion and of said varying up and down motion of said cutting tool 62 is shown diagrammatically in Figure 4 of the drawings which shows the path taken by said cutting tool 62 in making cuts in a plate 63 when said picture 2 is being scanned. As indicated by Figure 4, said cutting tool 62 will have a regular up and down motion of a stroke of predetermined length and frequency (or speed) and at the same time will move further into or completely out of said plate 63 in accordance with The operation of the apparatus shown in Figure 2 is similar to that of Figure 1 except that that part of the electrical system which is between said photo-electric cell 1 and said pushpull system which includes said power tubes I9 and 23 is arranged to do away with the aperiodic amplifying or direct; coupling connections between the several stages of the amplication system and provides an independent and easier means for adjusting each stage of amplication.

Said grid |6| of said tube |62 is kept at the cor- .grid |84, and as the potential of said grid |84 varies a similar potential variation but of amplied magnitude is generated across said secondary coil 202 of said transformer 200 and the current from said secondary coil 202 is transmitted by means of said detector tube 205 to the pushpull system which includes said power tubes I9 and 23. Said batteries 208 and 2 and said resistor |60 are ladjusted so that when a dark area is being scanned by said ,photoelectric cell 1 the current in said power tube 23 is at a maximum and the current in said tube I8 is at a minimum and whena light rarea is being scanned by said photoelectric cell 1 the current in said power tube 23 is at a minimum and the current in said power tube I9 is at a maximum. Since the plate current for said power tubes I9 and 23 is supplied by said battery 44 through said armature coil 39 the position of said armature 60 will be controlled by the lights and shades in the picture being scanned by said photoelectric cell 1, and any remaining carrier frequency current that is not eliminated by said condensers 220 and 223 will be by-passed around said armature coil 39 by said condenser |25,

Having thus described our invention, whatwe claim and desire to protect by Letters Patent is:

1. In apparatus for cutting screen-effect printing plates and having a cutting head comprising a tool holder, an armature in operative 'relation to move said tool holder and an electro-magnetic coil in operative relation to actuate said armature, a plate carrier in operative relation to the position of a tool in said tool-holder, and means for producing relative movement between said plate carrier and said cutting head, in combination, means comprising a photo-sensitive cell.

adapted to scan a picture to be reproduced and electrical connection :from said photo-sensitive cell to said electro-magnetic coil including means for connection t a source of power whereby variations in the conductivity of said photo-sensitive cell can cause corresponding variations in an electric current passing through said electromagnetic coil; means for producing synchronous relative movement between said plate carrier and said cutting head andbetween said scanning means and a picture to be scanned; and means for causing the oscillation of said armature and tool-holder at-a regular rate of speed through a path of oscillation having a constant length comprising a second photo-sensitive cell, electrical connection from said second photo-sensitive cell to said electro-magnetic coil including means for connection to a source of current, and means, in operated relation to said means for producing synchronous relative movement, for producing repeated and regularly timed changes in the conductivity of said second photo-sensitive cell alternately between a predetermined higher value and a, predetermined lower value.

2. In apparatus for cutting screen-effect printing plates and having a cutting head comprising a tool holder, an armature in operative relation to move said tool holder and an electro-magnetic coil in operative relation to actuate said armature, in combination means comprising a photosensitive cell adapted to scan avpicture to be reproduced and electrical connection from said photo-sensitive cell to said electro-magnetic coil including means for connection to a source of power whereby variations in the conductivity of said photo-sensitive cell can cause corresponding variations yin an electric current passing through said electro-magnetic coil and thereby to vary the position of said tool-holder; and means for causing the oscillation of said armature and toolholder at a regular rate of speed through .a

, path of oscillation having a. constant length comprising a second photo-sensitive \cell, electrical connections from said second photo-sensitive cell to said lelectro-magnetic coil including means for uconnection to a source of current, and means for 

